Thanks again for all of the great information Vance, it's been incredibly helpful.
I cleaned off (with both air and deoxit for connections) pretty much all of the electronics. After doing so, and letting everything dry, I've got a pretty interesting result. The unit still powers on, and when the volume switch is all the way a maximum, there's just the slightest bit of amplification going on. That is to say, I can hear the signal through the speaker, but it's only marginally louder than the tines sounding on their own. It's most noticeable in the bass register, where I can clearly hear the fundamental coming through the speaker (whereas the tines have a bunch of overtones going on).
I'm curious if you have any ideas that might account for this phenomenon? To my mind, it's clear that both the speaker and amp are working, at least to some extent. Just wondering if you might have any other thoughts on the matter, before I go ahead and try to find a tech who could work on this type of instrument around me. Thanks again, and hope you have a great weekend!